1. Technical Field
The present invention relates to an engine brake application system for an internal combustion engine having at least one cylinder, at least one exhaust valve associated with the cylinder, and a rocker arm for activating the exhaust valve wherein the rocker arm is arranged on a hollow rocker arm shaft. The present invention further relates to a method of reducing the engine speed of an internal combustion engine during gear shifts. The invention further relates to the use of a valve clearance take-up means for effecting engine braking.
2. Background Information
Commercial vehicles such as trucks and buses are increasingly being fitted with automatic or semi-automatic gearboxes. Such gearboxes are similar to conventional manual gearboxes, with the difference being that gear shifting is performed by actuators rather than manually by the driver. Appended FIG. 1 represents the principal phases of an upshift (i.e., to a higher gear) with such a gearbox. FIG. 1 is a comparison of engine torque and engine speed with respect to time. Phase xe2x80x9caxe2x80x9d represents a normal operating condition prior to instigation of a gearshift. Phase xe2x80x9cbxe2x80x9d represents torque removal once it has been determined that an upshift is to take place. Phase xe2x80x9ccxe2x80x9d represents disengagement of a dog clutch to disconnect the gearbox from the engine. Phase xe2x80x9cdxe2x80x9d represents reduction of engine speed to match the engine speed with the gear ratio to be selected. Once the engine speed has been reduced sufficiently, the new gear can be engaged. Thus, phase xe2x80x9cexe2x80x9d represents engaging the new dog clutch. Phase xe2x80x9cfxe2x80x9d represents reapplication of torque and phase xe2x80x9cgxe2x80x9d represents a normal operating condition after the gearshift has taken place.
In order to reduce loss of momentum of the vehicle during an upshift, it is advantageous to match engine speed with the new gear ratio as quickly as possible. It is known from Swedish Patent No. 502 154 C2 to selectively apply an exhaust gas brake during an upshift when certain operating parameters are attained, thereby effecting a rapid reduction of the engine speed. In this manner, wear on the exhaust gas brake system is said to be reduced since application of the exhaust gas brake occurs only during a small fraction of the total number of upshifts.
An auxiliary braking system for commercial vehicles is known from U.S. Pat. No. 5,193,497 (xe2x80x9cthe ""497 patentxe2x80x9d) in which an internal combustion engine is provided with a device for taking up valve clearance in the valve mechanism of the engine. The take-up occurs by means of an actively adjustable, hydraulically operated take-up means operable between two positions, namely a withdrawn position and an extended position. The take-up means is arranged at the operating end of the rocker arms whose valve clearance is to be taken up. In a manner described in detail in the ""497 patent, the engine""s existing pressurized oil system is used in order to guarantee operation of the device.
The auxiliary braking system disclosed in the ""497 patent has enjoyed considerable commercial success. However, due to the relatively long time it takes for the take-up means to attain its extended position, the system taught by the ""497 patent is not suitable for use for reducing engine speed during upshifts.
It is therefore an object of the present invention to provide an engine brake application system which incorporates the commercial advantages of the system described in the ""497 patent, and which is also suitable for use for reducing engine speed during upshifts. This object is achieved in accordance with the present invention by an engine brake application system for an internal combustion engine. The internal combustion engine should have at least one cylinder, at least one exhaust valve associated with the cylinder, and a rocker arm for activating the exhaust valve wherein the rocker arm is arranged on a hollow rocker arm shaft. The engine brake application system has a regulator or means for regulating oil pressure in the hollow rocker arm shaft, and a means responsive to an increase in oil pressure in the hollow rocker arm shaft and incorporated in the rocker arm for taking up clearance between the rocker arm and the exhaust valve. The system is able to effect valve clearance take-up by a means that is responsive to a signal generated in response to a need to effect a gear shift for rapidly increasing the oil pressure in the hollow rocker arm shaft.
It is a further object of the invention to provide a method for reducing engine speed during upshifts. This is achieved by a method for reducing engine speed of an internal combustion engine during gear shifts. The engine has at least one cylinder, at least one exhaust valve associated with the cylinder, a rocker arm that is arranged on a hollow rocker arm shaft for activating the exhaust valve, a regulator or means for regulating oil pressure in the hollow rocker arm shaft, and an actuator or means responsive to an increase in oil pressure in the hollow rocker arm shaft and incorporated in the rocker arm for taking up clearance between the rocker arm and the exhaust valve. The method requires generating a signal in response to a need to effect a gear shift, and rapidly increasing the oil pressure in the hollow rocker arm shaft in response to the signal to thereby effect valve clearance take-up.
The signal of the above described method may be generated in an Engine Management System. Further, in the above described method, rapidly increasing the oil pressure in the hollow rocker arm shaft may be accomplished by the use of a pneumatic actuator.
The invention also provides for the use of a valve clearance take-up means in an internal combustion engine for reducing engine speed during a gear shift.
Advantageous embodiments of the invention further include a means responsive to an increase in oil pressure in the hollow rocker arm shaft and incorporated in the rocker arm for taking up clearance between the rocker arm and the exhaust valve wherein the means is a pneumatic actuator. The pneumatic actuator may be arranged to inject a volume of oil into the hollow rocker arm shaft wherein the volume of oil is equivalent to a swept volume between a withdrawn position and an extended position of a piston.
Further, the pneumatic actuator may have an oil displacement means that is displaceable between a rest position and an activated position. The oil displacement means is preferably urged towards the rest position by a return means. The oil displacement means is preferably a piston, and the return means is preferably a resilient means such as a spring. In another embodiment, the oil displacement means and return means is a flexible membrane.
The oil displacement means is able to be displaced by the system from its rest to activated position in less than about 0.8 seconds; preferably in less than about 0.5 seconds; more preferably in less than about 0.2 seconds; even more preferably in less than about 0.1 seconds; and most preferably in less than about 0.05 seconds. The oil displacement means is able to be displaced by the return means from its rest to activated position in less than about 0.8 seconds; preferably in less than about 0.5 seconds; more preferably in less than about 0.2 seconds; even more preferably in less than about 0.1 seconds; and most preferably in less than about 0.05 seconds.